Fig. 2

Morphology of primary neurites of the histaminergic neurons in Thermobia domestica. Maximum projections of cLSM stacks (a–f, h–l: ventral view, anterior to the top; g: sagittal view, anterior to the left, ventral to the bottom). a–f Ventral-to-dorsal series of maximum projections revealed a contralateral projection associated to medial cell bodies (MC). a shows the complete stack, which is split in b to f. Same arrow types point to the same positions throughout the series (e.g., grey arrows in a, c, d). g Sagittal view of the metathoracic (MTG), first and second abdominal ganglia (AG1–2), showing the dorsomedial projections of the MC (black arrowheads). A strongly labeled longitudinal tract consisting of several axons is also visible (black arrows). h Projections of the MC in the abdominal ganglia. The primary neurite splits shortly after leaving the cell body in an ipsilateral and a contralateral branch (black arrows). i, j The large anterolateral cell bodies in the prothoracic ganglion projected medially (black arrowheads). Shortly after leaving the cell body, the primary neurite split into an ipsilateral branch, which entered the anterior connective (black arrows). The other branch projected further medially, crossing the ganglionic midline (dashed line) and entered the contralateral anterior connective (black double arrowheads). k, l One longitudinal tract projects without any specific branching through the ganglia (grey arrows in k). A second tract (black arrows in k and l), showed a medial horizontal branch (black double arrowhead in l) toward the ganglionic midline (dashed line). Ipsilaterally to the midline, this horizontal branch split again in a faintly labeled anterior and posterior tract (black arrowheads in l). Abbreviations: AG1–2: abdominal ganglia 1–2; ALC: anterolateral cell bodies; MC: medial cell bodies; MTG: metathoracic ganglion. Scale bars: a-f, i-l: 25 μm; g: 50 μm; h: 20 μm